Press release A team effort Deutsche Edelstahlwerke supplies steel wool manufacturers with primary material optimally tailored to their applications Noise is the number one environmental problem. Noise makes people ill – especially people who live near busy streets. And the hum on these streets is thunderous. In 2007 roughly 55.5 million automobiles were registered in Germany, and this trend is on an upward rise. The same is true for noise pollution as well. The amount is decisive because every new car today is equipped with modern muffler systems which are mostly based on a combination of reflection and absorption mufflers. Together they are able to reduce engine noise by approximately 20 to 30 percent. The major share of this reduction is achieved by the absorption muffler in which sound from a perforated exhaust pipe reaches a sound-absorbing layer. It is the heart of the muffler and is made of either glass or, more commonly, steel wool. Deutsche Edelstahlwerke GmbH is one of the few companies in Germany which produces the primary material for this steel wool: specialty steel wire 3.1 to 3.25 millimetres in diameter. This production requires optimal coordination of the individual processes because technical methods for subjecting the end product to final error checking have not been available in this size range up to now. Since the 1950s the company – called Stahlwerke Südwestfalen back then – has manufactured specialty steel wire which was used to make steel wool employed in large industrial facilities as well as household applications. For example steel wool pads were very popular as practical scouring pads. When the automobile industry finally discovered steel wool made of specialty steel as a lining material for mufflers, a major growth market opened up for the specialty steel producer based in Hagen thanks to its many years of experience in wire production. Specialty steel wire used for shaving steel wool must meet very specific requirements in the automobile industry. After all, it is employed within the exhaust gas system in an environment which is characterised by extreme thermal and corrosion stresses. "We developed material 1.4113 especially for this application", explains Karl-Heinz Heuser, head of wire research & development at Deutsche Edelstahlwerke. "It is a ferritic chromium steel supplemented with sulphur and molybdenum which has a high temperature and corrosion resistance and good machining properties as well." The latter is a decisive criterion primarily for Deutsche Edelstahlwerke customers which use the wire to make specialty steel wool on large cutting machines. When wire has better machining properties, this reduces residual segments in the machines and extends the service life of these machines. "Of course higher-alloyed materials are also suitable, but 1.4113 offers our customers the best price-performance ratio without compromising quality", says Heuser. Therefore its high economic efficiency is another reason why 1.4113 evolved into a popular standardised material for steel wool. In 2008 over 600 tonnes of bare wire of material 1.4113 were shipped from the factory in Hagen. That is not exactly a small proportion of the world’s largest product range in the long specialty steel product segment. It is certainly not small when you consider that 50 tonnes of specialty steel are used to produce about 35 tonnes of steel wool which can be used to equip up to 80,000 mufflers. Produced with know-how from the start – from scrap metal to specialty steel wire A lot of work has to be done, however, before the steel wool is finally installed in the mufflers, and the plants and employees of Deutsche Edelstahlwerke are at the beginning of this process. It starts at the production location in Siegen, which also belongs to Deutsche Edelstahlwerke like the ones in Witten, Krefeld and Hagen. Scrap is melted in a 130 tonne electric arc furnace at the steelworks there and then undergoes secondary metallurgic treatment by adding the necessary alloy components. These include e.g. carbon, silicium, manganese, sulphur, chromium and molybdenum. The right ratio of chromium, sulfur, manganese and molybdenum is required to produce the desired material properties for 1.4113. "If, for example, too much sulphur is added to the molten steel at the wrong time, inclusions can occur which make the wire tear faster afterwards. Then powder is created and not metal fibres", says Karl-Heinz Heuser. After melting and secondary metallurgic treatment, which takes about 80 to 100 minutes on average, the liquid steel is cast into 138 millimetre square billets in the S-type continuous casting machine. A total of six lines are operated by means of a dispensing chute. Afterwards the billets are transported by railway to Hagen where they are heated in an elevating hearth furnace. After a throughput time of approx. 1 hour, the billets reach the specified rolling temperature of 1100°C. Rolling begins in a reversing three-high stand with 10 passes (infeed 138 mm square billets, discharge 60x40 mm oval billets). After the material passes through the intermediate rolling train via a two-high stand and through a 10-stand "Kocks block", it is finally rolled on the 8-stand wire production block driven with 3,200 kilowatts. At this point the diameter of the wire is 5.5 millimetres. The most important ingredient in the recipe for success: Qualified employees In the next production step the wire bar coils are subjected to a special heat treatment at the Deutsche Edelstahlwerke plant. The company has amassed a large proportion of its special know- how at this station because the required wire properties can only be obtained through a very specific series of individual heat treatment steps. "The toughness of the wire is very important for our application. We use a special combination of heating, annealing and quenching steps to achieve this toughness even at high strengths", says Mr Heuser, explaining the heat treatment processes in a very simple manner. He refuses to reveal any more details, however. "This special heat treatment is not used by any other wire producer. It is a speciality of Deutsche Edelstahlwerke." The wire is pickled after the heat treatment to remove the scale layer. The plant in Hagen has a mixed acid pickling line which is filled with saltpetre/hydrogen fluoride mixtures at various temperatures and in different concentrations. The metal fibre wire is conveyed through the pickling line using hooks and dipped into 11 different tanks during this process. After pickling, the wire must pass through the next step to obtain its final diameter of 3.1 millimetres. During this step it runs through a multiple drawing machine with up to 11 drawing dies. The wire is subjected to a forming degree of approx. 50% during this process. This sounds simpler than it is because this process requires the utmost attention and concentration from the steel specialist. Ernst Haiss, managing director of Ernst Haiss GmbH in the third generation, knows this, too. Since 1924 the company has produced steel wool in many grain sizes which are exported to over 30 countries today. Companies from the mechanical engineering sector and the automobile industry are amongst its principal customers. Since 1973 Ernst Haiss GmbH has been purchasing the primary material for its speciality "specialty steel wool" from the specialty steel producer in Hagen, today Deutsche Edelstahlwerke. "Back then, the automobile industry started using specialty steel wool in mufflers. The specialty steel producer’s many years of experience in metal fibre production convinced us at that time", says Ernst Haiss about the beginnings of their collaboration. Know-how he still trusts in today. "The automobile industry has strict requirements regarding our steel wool. The diameter of the wire must not be greater than 3.1 millimetres or smaller than 3.0 millimetres in any case. This requires utmost attention and concentration from the wire drawer. He or she has to change the drawing dye in time to prevent the wire from becoming oval in its cross section and to ensure that the diameter of the wire is 3.1 millimetres at every point of the wire as specified. There can’t be any surface defects because they cause the material to break prematurely during cutting on our machines", says Haiss. This is a case which would mean a lot of work and expenses for the company. After the wire leaves the factory in Hagen, it is cut on approx.30 meter long, 3 meter high and wide machines at the Haiss GmbH plants. The wire is split lengthwise during a turning process in which the material moves over the cutting tools. If it broke during this process, the complete wire after the breaking point would have to be removed and refitted again. This costs the company a lot of time and money. "Today it is only possible to detect holes which are at least 10 millimetres long with the aid of modern testing methods. Because there are no technical testing methods for smaller defect dimensions, it is all the more important that the processes at our supplier, Deutsche Edelstahlwerke, are error-free from the start. When it comes to this product, you can only produce quality, not check it", stresses the managing director of Haiss GmbH. He values Deutsche Edelstahlwerke’s close collaboration with him as a customer: "From the beginning we have conducted joint test runs repeatedly to continuously optimise the production processes – starting with the steel melt – and the quality of the material according to our requirements. In this manner we keep improving ourselves together." Conclusion Deutsche Edelstahlwerke GmbH is the leading producer of long specialty steel products in the tool steel, high-grade construction steel as well as the stainless, acid-resistant and heat-resistant steel segments. The company has more than 50 years of experience in the production of specialty steel wires. They are supplied to customers from many different industries, e.g. the cleaning supplies industry or the medical technology industry. Its principal customers, however, are mechanical engineering companies and automobile industry suppliers which produce steel wool, among other products, from the metal wire. This is used, for example, in mufflers and contributes substantially to the reduction of noise on Germany’s roads. The optimal material for this purpose is the specialty steel 1.4113, which lends itself well to machining, is corrosion- and heat-resistant yet very economical. In the widest product range that can be found in the field of long specialty steel products anywhere in the world, the production of speciality steel wires requires special precision, know-how and monitoring by steel experts outside fully automated, mechanical operations. The required quality can only be assured by complying with and monitoring continuously developing process parameters. The customers of Deutsche Edelstahlwerke, including Ernst Haiss GmbH, therefore benefit from the one-stop production chain – from scrap metal to wire – and their involvement in the development of processes and materials.